The present invention relates generally to methods and apparatus for analyzing multifiber ferrules and, more particularly, to methods and apparatus for analyzing the end face of a multifiber ferrule.
With the increasing proliferation of optical communications and data transfer, multifiber connectors are becoming increasingly prevalent for interconnecting a plurality of optical fibers. As such, a number of multifiber ferrules have been developed. For example, one multifiber ferrule is the MT family of ferrules that has a generally rectangular shape in lateral cross-section. Another multifiber ferrule is the SC-DC ferrule that has a generally circular shape in lateral cross-section and is supplied by Siecor Corporation of Hickory, N.C., the assignee of the present invention.
In order to interconnect a plurality of optical fibers with a minimum amount of attenuation, a pair of multifiber connectors are preferably mated such that the optical fibers are biased into contact with one another. In order to provide proper fiber-to-fiber contact, the multifiber connectors must be precisely aligned in order to correspondingly align the individual optical fibers in the connectors. This alignment is typically provided by guide pins that extend outwardly from the end face of a male multifiber ferrule for insertion into corresponding guide pin holes, grooves, or other structures defined by a female multifiber ferrule. In addition to precise alignment, the polish geometry of the ferrule and, in particular, the polish geometry of the end face of the ferrule is extremely important to insure proper fiber-to-fiber contact. In this regard, at least the portion of the end face of each ferrule that is proximate the bores through which the optical fibers extend (hereinafter the xe2x80x9coptical fiber boresxe2x80x9d) is preferably polished to define a plane extending perpendicular to the axes defined by the guide pin holes and, therefore, perpendicular to the optical fiber bores. In addition, the planar surface defined by the portion of the end face of each ferrule proximate the optical fiber bores is preferably precisely positioned relative to the ends of the optical fibers. For example, with proper polish geometry, the fibers will extend by a predetermined distance beyond the end face of the ferrule such that fiber-to-fiber contact can be established. If, however, the polished geometry is not precisely defined, fiber-to-fiber contact may be prevented or otherwise obstructed by contact between those portions of the end faces of the ferrules that extend beyond the ends of the optical fibers.
In order to monitor the polish geometry and the resulting quality of the ferrules, it is desirable to determine the planarity of the end face of the ferrule and the angle of the end face relative to the optical fibers upon which the ferrule is mounted. As such, exterior surfaces of the ferrule have typically been utilized as a point of reference. In this regard, the shoulder defined by the enlarged rear portion of an MT ferrule is typically utilized as a point of reference relative to the end face of the respective ferrule. One inspection technique therefore determines the planarity of the end face and the angle of the end face relative to a point of reference defined by the shoulder of the ferrule. Unfortunately, the exterior surfaces of a ferrule and, in particular, the shoulder defined by an MT ferrule is a secondary datum and has no direct relationship to the alignment or the orientation of the optical fibers. For example, the end face may be properly positioned with respect to the shoulder of the ferrule even though the end face is improperly positioned relative to the optical fibers. Likewise, the end face may be improperly positioned relative to the shoulder even through the end face is properly positioned with respect to the optical fibers. Moreover, the connector industry is gravitating toward fully preassembled connectors in which the exterior surfaces that are typically utilized for reference purposes, such as the shoulder of an MT ferrule, are inaccessible and are therefore unavailable for reference with respect to the polish geometry of the end face of the ferrule. Therefore, although techniques have previously been utilized in order to analyze the polish geometry of the end face of a ferrule, the precision with which fibers must be aligned and brought into contact and the increasing emphasis on the preassembly of connectors demand that new techniques for analyzing the polish geometry of the end face of ferrules and the resulting quality of the ferrules be developed.
The method and apparatus of the present invention is therefore capable of precisely determining the orientation of the axis of the guide pin hole defined by a ferrule, including a partially defined guide pin hole, i.e., a guide pin groove. Since the axis of the guide pin hole has a direct relationship to the alignment of the optical fibers, the axis of the guide pin hole is a primary datum. As such, the method and apparatus of the present invention can also precisely determine the end face angle of at least that portion of the end face of the ferrule that is proximate the optical fiber bores based upon the primary datum, i.e., the axis of the guide pin hole, without reference to secondary datum, i.e., external features of the ferrule.
According to the present invention, a measurement pin is initially positioned in a guide pin hole such that a first end of the measurement pin is disposed proximate the end face of the ferrule. As a result of the construction of the measurement pin and the relationship between the measurement pin and the guide pin hole, a reference plane defined by the first end of the measurement pin is disposed at a predetermined angle, such as 90xc2x0, with respect to the axis of the guide pin hole. The method and apparatus of the present invention then measures the reference plane defined by the first end of the measurement pin to thereby enable the orientation of the axis of the guide pin hole to be determined based upon the predetermined angle between the reference plane and the axis of the guide pin hole.
In addition to measuring the reference plane defined by the first end of the measurement pin, the method and apparatus of the present invention can also measure a plane defined by at least a portion of the end face of the ferrule. For a ferrule that defines a plurality of bores for receiving optical fibers, the method and apparatus of the present invention preferably measures a plane defined by a region of interest encompassing the plurality of bores. Based upon an angular difference between the reference plane defined by the first end of the measurement pin and the plane defined by the end face of the ferrule, the method and apparatus can precisely determine at least one end face angle.
Typically, the reference plane defined by the first end of the measurement pin defines a X, Y plane. As such, the determination of at least one end face angle preferably includes a determination of first and second end face angles. In this embodiment, the first end face angle is based upon the angular difference in the X direction between the reference plane defined by the first end of the measurement pin and the plane defined by the end face of the ferrule. Likewise, the second end face angle is based upon angular difference in the Y direction between the reference plane defined by the first end of the measurement pin and the plane defined by the end face of the ferrule. While the angular differences in the X and Y directions can be separately measured, the angular differences in the X and Y directions can be measured concurrently, if so desired.
The method and apparatus of the present invention can be utilized in conjunction with ferrules that completely define guide pin holes as well as ferrules that partially define guide pin holes. In addition, the method and apparatus of the present invention can utilize two or more measurement pins positioned within respective guide pin holes that cooperate to define the reference plane. In one embodiment in which the ferrule, such as an MT ferrule, completely defines a pair of guide pin holes, first and second measurement pins are inserted into respective guide pin holes such that the first end of each measurement pin is disposed proximate the end face of the ferrule. The method and apparatus of this embodiment of the present invention then measures the plane defined by the first end of each measurement pin and determines the average of the planes to define the reference plane. In another embodiment in which the ferrule, such as an SC-DC ferrule, partially defines a pair of guide pin holes in the form of a pair of grooves that extend lengthwise along the opposed side surfaces of the ferrule, the first and second measurement pins are initially positioned within each groove such that the first end of each measurement pin is proximate the end face of the ferrule. Thereafter, the measurement pins are secured within the respective grooves.
In order to efficiently determine the end face angle of a ferrule, the method and apparatus of the present invention is preferably automated. As such, the means for measuring the reference plane and the means for measuring the plane defined by at least a portion of the end face of the ferrule are typically selected from the group consisting of a interferometer and a profilometer. Additionally, the means for determining the end face angle generally includes a processor for automatically analyzing the data collected during the measurement of the reference plane defined by the first end of the measurement pin and the measurement of the plane defined by at least a portion of the end face of the ferrule.
By determining the orientation of the axis of a guide pin hole defined the ferrule based upon the reference plane defined by the first end of a measurement pin inserted within the guide pin hole, the method and apparatus of the present invention is able to determine an end face angle of the ferrule based upon a primary datum of the ferrule. That is, the method and apparatus of the present invention determines an end face angle of the ferrule based upon an element of the ferrule that serves to align the ferrule and, in turn, the optical fibers upon which the ferrule is mounted, thereby providing a more precise and reliable determination of the polish geometry, including the end face angle of the ferrule. In addition, by measuring the end face angle of a ferrule based upon a reference plane defined by a first end of the measurement pin, the method and apparatus of the present invention permits precise measurement of the end face angle following preassembly of the connector that renders most exterior surfaces of the ferrule inaccessible.